Power generators used in electrosurgical procedures deliver electrical energy to an electrosurgical tool for operating on the tissue of a patient. An active electrode of the tool, connected to the power generator, concentrates the delivery of the electrical energy to a relatively small region of tissue of the patient. The electrical energy typically includes energy in the radio frequency (RF) band. The concentration of electrical energy facilitates cutting or coagulation of the tissue of the patient. During typical operation of a monopolar electrosurgical device, an alternating electrical current from the generator flows from an active electrode to a return electrode by passing through the tissue and bodily fluids of a patient.
During an electrosurgical operation, different tissue types may be encountered, such as, for example, fat, connective, glandular and vascular tissues. Connective, glandular and vascular tissues can have similar characteristics in the way they react to electrical energy, specifically, they have similar characteristics of electrical impedance. Fat however; has significantly different electrical response characteristics. In particular, fat presents a higher impedance to the flow of electrical current than do the other types of tissues. The tissue of certain anatomical portions, or regions, of a patient""s body may be largely heterogeneous on a macroscopic scale, such as on a scale commensurate with that of an electrosurgical cutting tool. For example, breast tissue has this heterogeneous property and can be made up of all the tissue types discussed above, i.e., fatty, glandular, connective and vascular tissues. The variations in electrical impedance exhibited by these various tissue types can be problematic when attempting to perform electrosurgical cutting in such heterogeneous, or non-homogeneous, tissue.
In a typical electrosurgical procedure, the amount of electrical energy delivered by a power generator must be carefully controlled. If insufficient power is delivered by the power generator, the tissue cutting of the electrosurgical procedure will be inhibited. If more power than necessary is delivered by the power generator there may excessive, and unnecessary, collateral tissue damage making it more difficult to perform a histology on a sample and thereby decreasing the ability of a pathologist to diagnosis the sample, as well as resulting in a more difficult recovery by the patient in addition to other sequela. Using a regulated power generator helps control and stabilize the electrical energy delivered into the patient""s tissue. However, due to the different electrical response characteristics of the various tissue types that may be present, the energy coupled into the tissue may vary even if the power generator is regulated. Generally, typical RF power generators experience difficulty in cutting through fatty non-homogeneous tissue because of the non-homogeneous tissue types that are typically encountered.
In addition, typical RF power generators are only effective with tools having small cutting surfaces. Thus, during an electrosurgical procedure, if fat is encountered, a surgeon must perform surgical cuts by xe2x80x9cfeatheringxe2x80x9d, making repetitive shallow cuts with countertraction over the same area to attain a desired depth of cut. In addition, because typical power generators are only effective for tools with small cutting surfaces, the types of tools available to a surgeon during electrosurgery are limited.
There is a need in the art for improved electrosurgical RF power generators that can be used with electrosurgical tools that encounter non-homogeneous tissue, such as, for example, breast biopsy instruments. Electrosurgical tools, such as electrosurgical breast biopsy instruments, can present varying load requirements to an electrosurgical power generator than typical electrosurgical tools, due to the heterogeneous nature of the tissue they are used to cut or coagulate.
From the discussion above, it should be apparent that there is a need for an electrosurgical power generator used in electrosurgical procedures that will more effectively couple electrical energy to different types of tissue, in particular heterogeneous tissue that includes fat tissue. In addition, there is a need for a power generator that works effectively with large cutting surfaces, thereby expanding the types of tools that are available for electrosurgery.
The present invention satisfies these and other needs.
The invention is directed to a high frequency electrical power generator particularly suitable for use in electrosurgery.
An electrical power generator constructed in accordance with the invention is configured to produce electrical power at a frequency of about 1 MHz to about 14 MHz, preferably about 3 MHz to about 8 MHz. The electrical power generated preferably has an essentially sinusoidal waveform with a total harmonic distortion (THD) of less than 5%. The specified frequency and waveform help to minimize damage to adjacent tissue during electrosurgery. The power output has a high voltage level, for example, up to about 1,000 Vrms, and a high current level for example, between about 0.5 amps to 5 amps, particularly about 1 amp to 2 amps. The output of the electrosurgical power generator is connected to an electrosurgical tool configured to receive the voltage and current produced by the electrosurgical power generator and deliver the voltage and current to an electrosurgical site on a patient. There is preferably at least one ground pad in electrical contact with the patient to complete an electrical circuit for the system comprising the generator and the tool, thereby providing a controlled return path for the current from the electrosurgical site to the electrosurgical power generator.
The system may also include a distal interface pod, located proximate to the electrosurgical site, connected to the output of the high frequency electrosurgical generator. In one embodiment, the distal interface pod is configured to present a desired load to the electrosurgical power generator. In addition, the distal interface pod may include safety and patient interface functions, as well as telemetry functions such as monitoring various parameters important to safety as well as control parameters, for example, the voltage and current produced by the electrosurgical power generator and delivered to the electrosurgical tool.
The high frequency characteristics described above improve the electrosurgical power generator""s ability to deliver consistent power over a range of electrical impedance loads caused by variations in tissue types.
The high voltage characteristics described above facilitate the use of long electrodes during an electrosurgical procedure. Use of long electrodes may require substantially higher starting and sustaining voltages, particularly when fatty tissue is present, in contrast to when other types of tissue are encountered.
Electrical power output with an essentially sinusoidal waveform in an electrosurgical procedure concentrates the electrical power into cutting tissue, thereby reducing the total power required during the electrosurgical procedure. Reduction in total power results in less heating, and thereby less damage to collateral tissue. Total power delivered during an electrosurgical procedure may also be reduced through duty factoring where the power is turned xe2x80x9conxe2x80x9d and then xe2x80x9coffxe2x80x9d in rapid succession. When duty factoring the power output, the waveshape envelope may be, for example, a ramped, or trapezoidal rectangle, or a zero crossing switched rectangle.